Yoga says Wikipedia is a physical, mental and spiritual practice. Its origins go back to the pre-Vedic Indian traditions but most likely developed during the sixth and fifth centuries BCE. The Yoga Sutras of Patanjali written in the first half the first millennium CE is one of the key surviving texts composed of 196 Indian sutras (threads in English) or aphorisms.
Yoga as we know it today came to North America in 1893 when Swami Vivekandanda spoke at the World Parliament of Religions in Chicago where his message was greeted by a standing ovation by the assembly. In 1946, Paramahansa Yoganandya, after years of teaching in the West, wrote his Autobiography of a Yogi which remains to this day a popular spiritual classic.
B. K. S. Iyengar’s Light On Yoga has been very influential on the growth of yoga in North America. A free PDF version is available online.
A modern classic is Judith Lasater”s Living Your Yoga which is sub-titled “Finding the Spiritual in Everyday Life”.